The Wall Street Journal says Autopilot has lost 10 engineers and 4 top managers.

Self-driving cars are coming, and Tesla CEO Elon Musk has been pushing his engineers hard to make sure that Tesla stays on the cutting edge. Indeed, in October 2016 he promised that the latest version of the Model S and Model X—cars with Tesla's new "Hardware 2" suite of cameras and radar—would become capable of full self-driving in the future with just a software update.

But according to a new report from TheWall Street Journal, some Tesla engineers are skeptical that Tesla can keep this promise any time soon. Disagreement about deadlines—as well as "design and marketing decisions"—has caused turmoil on the Autopilot team.

"In recent months," the Journal reports, the Autopilot team "has lost at least 10 engineers and four top managers." That included the director of the Autopilot team, "who lasted less than six months before leaving in June."

Tesla told The Wall Street Journal that the company has simply been losing engineers to other technology companies hungry for workers with autonomous driving skills.

Tesla’s Autopilot has been dogged by safety concerns

TheWall Street Journal doesn't go into a lot of detail about why the Autopilot team has been losing talent. But we do know that over the last three years, Tesla has faced both internal and external warnings about the safety risk of pushing Autopilot technology forward too quickly.

"Weeks before the October 2015 release of Autopilot, an engineer who had worked on safety features warned Tesla that the product wasn’t ready," the Journal reports. In a resignation letter, the engineer, Evan Nakano, warned about "reckless decision making that has potentially put customer lives at risk."

Another engineer raised concerns after he experienced strange driving behavior with a prototype vehicle in May 2015. The car was driving so erratically that a police officer pulled him over, suspecting drunk driving. The engineer was sober, but he warned colleagues about problems with the vehicle. Later, he says, he was "dismissed for what he was told were 'performance issues.'"

Tesla also suffered an acrimonious split last year with MobileEye, an Israeli supplier of self-driving car technology, after Tesla customer Joshua Brown died in a fatal crash in May 2016. The passenger engaged autopilot, took his hands off the wheel, and ignored repeated warnings to grab the wheel. His car crashed into a semi-truck that turned in front of the vehicle.

In a September statement, MobileEye wrote that Tesla had been "pushing the envelope in terms of safety." Other carmakers had been more aggressive about disabling driver-assistance features if a driver refuses to put his hands on the wheel.

Since Brown's death, Tesla has tightened up these rules—the Model S will now pull over to the side of the road if the driver ignores three warnings to put his hands back on the wheel.

After its breakup with MobileEye, Tesla developed its own "Hardware 2" sensor package for use on the Model X and Model S. The big question is whether Tesla can keep its promise to enable full self-driving capabilities with these vehicles—and if these vehicles will actually be safer than human drivers.

That could be challenging because Tesla is attempting to develop self-driving technology that relies only on cameras and radar. Other companies, including Waymo, have built their self-driving technology around a lidar sensor. Lidar provides high-resolution 3D information about the surrounding environment, but a single lidar sensor can cost tens of thousands of dollars.

Tesla hopes it can achieve similar levels of safety and reliability with much cheaper cameras and radar sensors. But the turmoil in the company's Autopilot division suggests that effort may not be going smoothly.